TUTOR. An eclipse of the sun may be central, and not total; for, those who are under the point of the dark shadow, will see the edge of the sun like a fine luminous ring, all around the dark body of the moon when the sun is eclipsed at the moon’s greatest distance from the earth; but when she is nearest the earth at an eclipse of the sun, the eclipse is total. When the penumbra first touches the earth, the general eclipse begins; when it leaves the earth, the general eclipse ends. An eclipse of the moon always begins on the moon’s eastern side, and goes off on her western side; but an eclipse of the sun begins on the sun’s western side, and goes off on his eastern side. When the moon is eclipsed in either of her nodes, the eclipse is both central and total. PUPIL. Pray, what is the reason we have not an eclipse at every full and change of the moon? TUTOR. For the same reason that Mercury and Venus are not seen to pass over she sun’s disc at every inferior conjunction. PUPIL. Is the orbit of the moon then inclined to the plane of the ecliptic? TUTOR. It is: and no eclipse of the sun can happen but when the moon is within 17 degrees of either of her nodes: neither can there be one of the moon, unless she be within 12 degrees. At all other new moons she passeth either above or below the sun, as seen from the earth: and at all other full moons above or below the earth’s shadow, according as she is north or south of the ecliptic. You now see that the moon must sometimes rise before and sometimes after the sun at change, and before or after he sets at full. PUPIL. I do, Sir, and am much obliged to you for this pleasing account of the moon, and of eclipses: and if you have any thing farther to observe, it will afford me additional pleasure. TUTOR. You may, at some time or other, have an opportunity of seeing a total eclipse of the moon; it will therefore be necessary to prepare you for a phænomenon which otherwise you might be much surprized at, and that is, that after the moon is immersed in the earth’s shadow, she is still visible. PUPIL. This is a phænomenon that I am not able to account for; for, the moon being an opaque body, she cannot shine by her own light[16], and the rays of the sun are prevented falling on her by the interposition of the earth, she cannot therefore shine by reflection. [Footnote 16: Dr. Herschell supposes the moon and the rest of the planets may have some inherent light: the side of the planet Venus, turned from the sun, having been seen, as we see the moon soon after the change.] TUTOR. It is by reflection that we see her; for the rays of the sun which fall upon our atmosphere are refracted or bent into the earth’s shadow, and so falling upon the moon are reflected back to us. If we had no atmosphere, she would be totally dark, and of course invisible to us. PUPIL. What is her appearance?